Carriers of this type are also referred to as plating racks and serve for holding metal parts to be plated with an electric contact necessary for the plating operation such as hard chromium plating in a galvanic bath in which the parts are immersed. In order to avoid the labor intensive removing of parts from one carrier and attaching these parts to another carrier for different operational steps in a plating process, it is desirable to keep the parts held in place on the same carrier for all such steps as rinsing, roughening, plating, and drying. However, the prior art leaves substantial room for improvement in this respect.
The quality of the plating or coating, especially the thickness and the uniformity of the coating over the coated surface area is substantially influenced by the quality of the electrical contact between the part to be plated and the electrode holding the part in the bath during the plating operation. Any disturbances in the electrical contact adversely affect the coating or plating quality.
Even a small out-of-alignment positioning of a part relative to the current carrying section of the carrier also referred to as "electrode" can cause the plating current density to fall below the critical current density necessary for an effective electrolytic deposition. Such critical current densities are within the range of 20 to 80 A/cm.sup.2. Thus, the contact between the part and the electrode determines the reject quota in any particular plating batch.
Attempts have been made heretofore to improve the contacting between the part and the electrode by mechanical contact springs. However, such contact springs are not efficient where large number of parts are to be plated because mechanical damage to the clamped parts is hard to avoid and because the mounting of the parts to the electrode by the clamps is not only very labor intensive, it is also tedious work that has heretofore resisted automation.
A further problem is seen in the requirement that certain parts are to be plated only on a particular surface area while leaving other surface areas of the part free of the plating or coating. Efforts to solve this masking problem heretofore are also very labor intensive due to the use of masking tapes, masking lacquers, protective coatings or the like that must be applied prior to the galvanic plating operation.